Field of the Invention
The present invention relates to a radiation imaging apparatus, a radiation imaging system, and a radiation imaging method for acquiring offset correction data.
Description of the Related Art
In recent years, imaging apparatus in which a radiation image is converted into digital signals directly and in real time are popular as imaging apparatus configured to capture a radiation image with radiation rays transmitted through an object. For an observation of the interior of a relatively large object, such as human body, in particular, large-area flat panel radiation imaging apparatus (flat panel displays: FPDs) have been proposed.
Capturing a radiation image involves offset correction processing in order to remove an offset component due to residual charge, dark current charge accumulated during photographing, or fixed-pattern noise.
Common offset correction processing is performed by using image data that is acquired without the irradiation of radiation rays (non-exposure image data) as offset correction data and subtracting the non-exposure image data from radiation image data.
In U.S. Pat. No. 7,415,097, the order (a sequence) in which correction-use images (correction frames, in particular, offset frames) for a plurality of operating modes are acquired is discussed. Offset frames for operating modes that are determined as high in the frequency of use in a particular time slot are updated preferentially in the subsequent time slot, and this operation is repeated continuously. The frequency of use is determined by weighted averaging, based on the length of use and the number of times recording operation is executed.
In Japanese Patent Application Laid-Open No. 2013-118983, the order in which the necessity/non-necessity of execution is determined for offset correction modes is varied depending on what testing technique is selected at the time of photographing. The length of time elapsed since the last execution time till the time of determination is measured for every offset correction mode. An offset correction mode for which the elapsed time exceeds a given length of time is determined as a mode that needs to be executed, and an offset correction mode for which the elapsed time is within the given length of time is determined as a mode that does not need to be executed.
As described above, radiation imaging apparatus have a possibility of image quality deterioration from an offset component that is caused by residual charge and dark current charge, or by fixed-pattern noise. It is therefore necessary to execute offset correction processing by acquiring non-exposure image data as offset correction data.
Offset correction data in this case needs to be acquired (or updated) for each of a plurality of imaging modes. A problem is that, when offset correction data is acquired (or updated) for every imaging mode, a long period of time is required until a radiation image of an object can be captured.